1. Field Of The Invention
This invention relates to reciprocating pumps, and more particularly, to a pump having an eccentric gear drive mechanism with cam rollers positioned on an output shaft and engaging a cam roller track for guidance thereof.
2. Brief Description Of The Prior Art
Reciprocating, plunger type pumps are well known in the art, and such pumps typically use a crankshaft, connecting rods and crossheads to actuate the plungers. A typical example of such a pump is the Halliburton HT-400 which is used as a multi-purpose pump for a variety of drilling fluids, including drilling muds. Conventional reciprocating pumps have well known unbalanced forces which require a substantial structure to support the pump and its drive mechanism. The eccentric gear mechanism of the present invention provides a design in which the kinematics are such that it is possible to use a lighter weight support structure than with a conventional crankshaft driven pump of similar horsepower and plunger load capacity.
Crankshaft driven pumps generally require the use of journal bearings which are between the connecting rods and crankshaft. This is avoided in the present invention because the eccentric gear design allows ball or roller bearing mounting of the gears. The sliding contact of the prior art pump crosshead within its crosshead guide is eliminated because no crosshead is required for the eccentric gear design. Thus, major areas of wear in conventional pumps are eliminated with the present invention.
Another factor in the design of conventional, crankshaft driven pumps is that when a long stroke is required, corresponding longer throws on the crankshaft are necessary. In the present invention with the dual eccentric gear design, the displacement comes from each of a set of gears rather than from one crankshaft throw. Thus, a more compact structure is possible than with conventional pumps of the same stroke. The pump of the present invention therefore solves many of the problems and addresses the limitations of conventional pumps.
U.S. Pat. No. 2,534,428 discloses a power jack for pumps with gears mounted in a gear wheel mounting member. Each of the gears has an annular groove or guideway in the outer periphery thereof. The gear wheel mounting member has two apertures and is split so that it can be placed in the guideways in the gears. The inside diameters of the apertures act as bearings in which the outwardly facing surfaces of the grooves and the gears rotate. During rotation, the drive shaft remains fixed vertically and horizontally. In an alternate embodiment, the gear wheel mounting member totally encloses the gear wheels. Extending transversely on the gears are "marginal portions" which form annular shoulders or guideways on both sides of the gear teeth. These guideways are received in apertures in the mounting member which act as bearings. In the present invention, a somewhat similar arrangement is used, but roller or ball bearings are provided on the gears. Further, the present invention includes a cam roller engaged with a cam roller track for support and guiding of the apparatus, a feature which is not shown in Cruikshank.
U.S. Pat. No. 1,318,130 to Barton discloses a vertically reciprocating pump having a pair of elliptical gears which are intermeshed to reciprocate a frame of a pump. An obvious problem with this mechanism is that such eccentric shaped gears would be much more difficult to make than the circular gears of the present invention or Cruikshank. In Barton, upright portions of the reciprocating frame have slots therein which are guided on the drive shaft. The gears have a shroud portion on opposite sides of the two portions thereof, and these shrouds act as cam surfaces on which the two gears ride.